Those and similar options shall restrict the area in which schematics are rendered.
Use case: If you work on something large you can either have all blocks opaque rendered, then you very fast lose yourself in a labyrinth of schematic blocks (sure, just repeatedly toggling would work aswell) or you switch to translucent blocks. But there, as you get huge loads of stacked ghost blocks it's sometimes quite difficult to differentiate different blocks. These suggestions restrict rendering of schematics to a certain shape/area which moves relatively to the player. In case of the sphere, anything which is less than x blocks away from the player. -1 would automatically refer to the current infinite mode and 0 would mean to only render the block at the player's head position. (=> 0 = Kinda useless) Scrolling through that radius would enhance the user experience aswell I guess.

Only rendering the schematic inside an area selection is already on the TODO list, I guess I can also add a sphere mode to the list. What would the ray move do? Just render blocks along the ray trace vector? I would kind of imagine that being somewhat pointless, because then you are only properly seeing one block and then a bunch of stuff is hidden behind it.

I'm unsure how helpful even the Sphere mode would be though... Usually you simply don't want to be inside a huge mess of schematic blocks, but just outside of the rendered area. Unless it's like an aesthetic building, in which case you can be inside the rooms and stuff and properly still see what you are doing, but in that case even the normal All mode works. Are the current Single Layer, Layer Range or All Above/All Below modes not suitable for your use case?

There is also a "player-following" option (I think it's in Generic atm in the 1.13.2+ versions), which makes the "render boundary" or the layer range move together with the player's movement. That option was also somewhat recently fixed/improved in the 1.12.2 version, so that it doesn't collapse the Layer Range mode's range anymore, and it now also has an offset option, so you can decide how exactly it relates to the player position.

Usually you simply don't want to be inside a huge mess of schematic blocks

And from my experience - only all below and all above modes were ever useful for standing just outside.

Though it would help to have earthier way to switch axis. And maybe all except range mode.

Also maybe way to turn off some of modes you don't use, to switch between them faster?

well I didn't know about the "player-following" property. That's nice. Couldn't check yet, but do I have the option to lock the tracking in a subset of directions? Like, lock x and y and only have z following. For Sphere and Ray, those were kind of arbitrary suggestions. But for the time being I'm missing a vertical layer mode (i.e. you see all blocks in the layers in front of you) so that you can build structures back to front instead of bottom up. Especially for smaller structures that'd be very convenient to only see the schematics as a wall rather than a floor or everywhere around me. And for the following part, the offset is crucial, thanks for mentioning it.

Especially for smaller structures that'd be very convenient to only see the schematics as a wall rather than a floor or everywhere around me.

If i understand right... all above/below layer mode + switch axis to X or Z (in last menu in M+C).
Mind you, especially when you go for X or Z axis - single layer would usually display not enough info, as blocks on layer bellow can affect block on current layer. That's not only redstone, because, at least, stairs.

Also in my experience - area following player isn't that comfortable. Especially when u need to place a lot of curvy stairs, because you are going back and forth, closer and farther from layer you currently building.
So when current layer follow you it would constantly flicker.

What i use instead - i've assigned easily accessible buttons to layer prev/next, arrow key up and down.
That way i move current layer only when i need to. But when i do need - it's fast and easy.